The present invention relates generally to two spool gas turbine engines and more particularly to a two spool gas turbine engine having a synchronizing stationary clutch system used for energy dissipation, compression braking or starting of the gas turbine engine.
A two spool gas turbine engine has two independent, uncoupled main shafts, with the gas generation system on one shaft and independent power turbine on the second shaft. This mechanically uncoupled arrangement allows independent control of the power turbine speed and consequently more efficient operation of the power output of the engine, resulting in greater fuel economy. The engine is normally used to drive an engine gearbox mounted electric generator. The generator, in turn, charges batteries that power the land vehicle's drive sprocket mounted electric motors.
Once in motion, a conventional braking device can be used to slow or stop the land vehicle. However, if continuous or prolonged braking is required, such as when the vehicle is moving downhill, there is considerable heating and wear on the brake parts. In most diesel driven conventional transport semi trucks, braking is assisted by releasing the compressed air in the diesel engine's cylinders to the exhaust during the compression stroke. However, no such system for slowing a vehicle without conventional braking is used in two spool gas turbine engines.
The prior art discloses a number of systems for coupling two independent shafts in gas turbine engines. U.S. Pat. No. 4,642,029 discloses a braking system for stopping the rotation of counter rotating blade members of a gas turbine engine used in aircraft. The brake system comprises a clutch that allows simultaneous retardation of the rotation of two transfer shafts and, thereby, both rotating blade members. However, the brake system is designed to be used after the engine has been turned off and the blades need to stop rotating for noise and safety reasons. It does not disclose a system that allows for backdriving or slowing of an engine that is operating.
U.S. Pat. No. 5,577,973 discloses a transmission that provides for the differential of two or three separate and otherwise mechanically uncoupled prime movers in a hybrid arrangement. However, the coupling of the movers converts the constant speed of one of the prime movers into variable components of torque and speed as required for vehicle function but does not result in a braking or slowing of a vehicle.
As can be seen, there is a need for a system that allows backdriving or compression braking of a two spool gas turbine engine to control the speed a land vehicle while decreasing wear on the conventional braking system of the vehicle. Such a system may also be used to start the engine and/or retard an oversped turbine so as to eliminate the need for separate systems for those functions.